Conventionally, a negative pressure abnormality detection apparatus has been known that determines whether a negative pressure sensor is abnormal (see, for example, Patent Document 1). Such an abnormality detection apparatus includes a negative pressure sensor that outputs a signal depending on negative pressure, and detects the negative pressure based on the signal from the negative pressure sensor. Then, based on a result of the negative pressure detection, the apparatus determines whether the negative pressure sensor is abnormal. Specifically, the apparatus determines that the negative pressure sensor is in an abnormal state if a state continues for a predetermined time or longer during which the signal from the negative pressure sensor deviates out of a desired normal range due to a disconnection, a power short, a ground short, etc.
Also, a vehicle having the negative pressure abnormality detection apparatus installed, which is described in Patent Document 1, includes a brake booster that assists a braking operation by the driver, by using intake negative pressure of an intake manifold that is generated by rotation of an internal combustion engine (referred to as “inmani negative pressure” below). Also, this vehicle is a stop-and-start control vehicle that has the internal combustion engine stop automatically if a predetermined stopping condition is satisfied, and after the automatic stopping, has the internal combustion engine restart automatically if a predetermined restarting condition is satisfied. Then, if the negative pressure sensor is determined to be in an abnormal state as described above, automatic stopping of the internal combustion engine is inhibited.
Incidentally, while the negative pressure sensor still outputs the signal that changes depending on the negative pressure, an abnormality may occur with the negative pressure sensor that includes, in addition to a disconnection, a power short, or a ground short described above, an abnormality due to deviation in which a gain shift or an offset shift is generated that may be caused by the temperature characteristic or change over the years. However, the control apparatus described in Patent Document 1 cannot determine that an abnormality occurs until reaching a state where the output signal of the negative pressure sensor deviates out of the desired normal range. Therefore, if the output signal of the negative pressure sensor has a gain shift or an offset shift, but the shift is comparatively small such that it is contained within the desired normal range, the control apparatus cannot detect the abnormality due to deviation of the negative pressure sensor. Therefore, even if an abnormality due to deviation occurs with the negative pressure sensor, the abnormality due to deviation may not be detected as an abnormality of the negative pressure sensor.
Thereupon, to determine whether an abnormality due to deviation occurs with the negative pressure sensor, one may consider a method that has the internal combustion engine rotate for generating an inmani negative pressure; determines whether the detected negative pressure value based on a signal from the negative pressure sensor is shifted toward the positive pressure side or the vacuum pressure side with respect to a threshold; and based on the shift, determines whether an abnormality due to deviation occurs with the negative pressure sensor.